Process for catalytically reacting gases having a high SO{HD 2 {B content using different catalysts

ABSTRACT

Gases having a high SO2 content are catalytically reacted with oxygen in catalyst contacting trays to form SO3. The catalyst in the first contacting tray is different from the catalyst in the second contacting tray. The feedstock gases are reacted in the first contacting tray in contact with a vanadium pentoxide based catalyst and the effluent gas from the first contacting tray is fed to a second contacting tray without interstage cooling and is reacted therein in contact with an iron oxide based catalyst.

United States Patent 1191 Reh et al.

[ 1 PROCESS FOR CAT ALYTICALLY REACTING GASES HAVING A HIGH S0 CONTENTUSING DIFFERENT CATALYSTS [75] Inventors: Lothar Reh, Bergen-Enkheim;

Karl-Heinz Dorr, Mainz; Hugo Grimm, Frankfurt am Main; Karel Vydra, BadNauheim, all of Germany [73] Assignee: MetallgesellschaftAktiengesellschaft,

Frankfurt am Main, Germany 22 Filed: Mar. 21, 1973 21 Appl. No.: 343,584

[30] Foreign Application Priority Data Mar. 21, 1972 Germany 2213580[52] U.S. Cl 423/534; 423/522 [51] Int. Cl C01b 17/78 [58] Field ofSearch 423/521, 522, 528, 532,

[56] References Cited UNITED STATES PATENTS 690,133 12/1901 Clemm et a1.423/534 1 July 29, 1975 729,735 6/1903 Clcmm et al. 423/534 19659637/1934 Merrian 423/533 2,042,675 7/1936 Merrian 423/528 3,005,68710/1961 Udy 423/522 FOREIGN PATENTS OR APPLICATIONS 46-30089 1/1971Japan 423/534 Primary ExaminerO. R. Vertiz Assistant Examiner-Gary P.Straub Attorney, Agent, or Firm-Burgess, Dinklage & Sprung [57] ABSTRACT6 Claims, 3 Drawing Figures PATENTEUJULESISYS SHEET PATENTED JUL29 I975SHEET my. a

PROCESS FOR CATALYTICALLY REACTING GASES HAVING A HIGH S CONTENT USINGDIFFERENT CATALYSTS BACKGROUND This invention relates to a process forcatalytically reacting gases having a high S0 content with oxygencatalyst containing contacting trays to form S0 wherein the firstcontacting tray contains a catalyst which differs from that in thesecond contacting tray.

During the reaction of SO -containing gases to form S0 which issubsequently used to produce sulfuric acid, the catalyst must be heatedfirst by the gas to the so-called initiation temperature. Thisinitiation temperature depends on the composition of the catalyst and onthe process by which it has been made and, e.g., with catalysts based onvanadium pentoxide (V 0 is about 400450C. The reaction of S0 to form30;, results in a temperature rise because the reaction is exothermic.With gases which contain up to about 11 $0 the reaction is arrested attemperatures of about 620C., where the equilibrium of the reaction S0/2O S0 is reached. With gases having a higher S0 content, thetemperature continues to rise because the reaction reaches itsequilibrium only at higher temperatures. However, the catalyst willdeteriorate at temperatures above about 620C.

Several processes of heating gases having a high S0 content have beenproposed whereby deterioration of the catalyst by overheating isavoided. For instance, it is known to reduce the S0 content of the feedgases by admixing partly reacted gases, which contain S0 with thestarting gases (DAS No. 1,054,431; German Pat. No. 504,635; DOS No.2,026,818). In these processes, however, gas must be passed through thecontactin g trays at a high rate which increases with the S0 content. Itis also difficult technologically to accomplish a uniform blending ofthe gases and the contacting vessel must be larger in accordance withthe gas recycle rate.

It is also known to react gases which contain up to 14% S0 underconditions involving a deficiency of oxygen and to supply cold dry airto the gases in stages in order to cool the gases and to add oxygenthereto (U.S. Pat. No. 2,180,727).

This process has the following disadvantages: In the case of a moderateS0 content, a temperature rise above the range which is permissible forthe catalyst may be prevented by a control of the oxygen deficiency butair must be added at an automatically controlled rate after eachcontacting tray. In the case of higher S0 content, e.g., above 20%, airmust be admixed and in addition thereto the gases must be subjected toan indirect interstage cooling between the several contacting traysbecause a cooling only by an injection of air would result in an oxygensurplus and unpermissible temperature rise in the next contacting tray.A considerable expenditure is required for the admixing of the air tothe gas with the uniformity which is required.

It is also known in the case of gases which contain about 8-1 1% S0 toconduct a partial stream at a velocity of flow of 0.62 meters per secondthrough a preliminary contacting tray, which precedes the maincontacting tray, whereafter the SO -containing gases which leave thepreliminary contacting tray are admixed with colder gases which containS0 and the mixed gases are reacted in the conventional manner in themain contacting tray (Austrian Pat. application No. 10932/68). In thisprocess, a separate preliminary contacting tray is required and highlyconcentrated gases cannot be treated unless a plurality of preliminarycontacting trays are provided.

In connection with the reaction of SO -containing gases in a contactingtray, it is also known to control the peak temperature by varying the V0 content of the catalysts I-Ielv. chim. Akta 24, Reprint No. 71 E 79 E,13/12, 1941, Basel, Ges. f. chem. lnd.). If that process were used totreat gases having a high SO content, the reaction would have to beinterrupted when a temperature of about 620C. has been reached, and aninterstage cooling would then be required.

If these processes, only a relatively limited temperature range, and inconjunction therewith, only a limited conversion range is available foreach contacting tray because the reaction is adiabatic. Where catalystsbased on vanadium pentoxide (V 0 are used, that temperature range isfrom about 400 to 620C. When the upper temperature limit has beenreached, thereaction in each contacting tray must be interrupted and thegases must be subjected to interstage cooling before they may beadmitted into the next contacting tray.

It is also known to provide series-connected contacting trays whichcontain different catalysts. In these processes (German Pat. No.136,134, German Pat. No. 682,915, U.S. Pat. No. 1,965,963, U.S. Pat. No.2,042,675), the first contacting tray is operated at a highertemperature than the second contacting tray. Besides, these processesare not used to treat gases having a high S0 content. Disadvantageswould be involved in the use of these processes to treat gases having ahigh S0 content.

SUMMARY It is an object of the invention to avoid or reduce in theprocessing of gases having a high S0 content the disadvantages of theknown processes and specifically to reduce the number of interstagecooling steps previously required between the contacting trays for agiven total conversion and yet to avoid a deterioration of thecatalysts.

Thus, the invention provides a process for catalystically reacting gaseshaving a high SO content with oxygen in catalyst contacting trays toform S0 wherein the catalyst in the first contacting tray is differentfrom the catalyst in the second contacting tray. Included in the processof the invention are the steps of reacting said gases in the firstcontacting tray in contact with a vanadium pentoxide based catalyst andfeeding the effluent gases from the first contacting tray to the secondcontacting tray without interstage cooling and reacting said effluentgases therein in contact with an iron oxide based catalyst.

DESCRIPTION OF THE DRAWING The present invention will be more fullyunderstood from the following description taken in conjunction with theaccompanying drawing wherein FIGS. 1-3 are graphs plotting theconversion of S0 to S0 against temperature.

DESCRIPTION The process according to the invention may be used to treatgases which contain about 11-60% S0 The second contacting tray may bedisposed directly above or below the first contacting tray so that bothcontacting trays constitute a double contacting tray. The gases areadmitted into the first contacting tray at the operating temperature ofthe catalyst. This is usually somewhat higher than the initiationtemperature of the catalyst concerned. The reaction is conducted untilthe temperature has increased to the highest value which is permissiblewithout a deterioration of the catalyst, or to a lower temperature,which results in an optimum conversion. This temperature is controlledby a selection of a suitable residence time of the gas in the contactingtray. The residence time is controlled so that S is converted into S0 tosuch an extent that the temperature rises only to the values stated. Atthis temperature, the gases are directly transferred into the secondcontacting tray, in which they are reacted fur ther, preferably to theequilibrim temperature because these catalysts will not be deterioratedunless heated to much higher temperatures.

In the contacting tray which contains a catalyst based on vanadiumpentoxide, the V 0 content of the catalyst is preferably selected inaccordance with the known method so that the rate of the reaction S0 /2O 80;, is reduced so as to provide for a technologically desirableresidence time. Besides, the reaction rate may be reduced by an additionof reactionretarding substances, such as manganese oxide.

According to a preferred feature, the reaction in the first contactingtray is conducted until a temperature of about 550620C. has been reachedand the reaction in the second contacting tray is conducted until atemperature of about 690760C. has been reached. Particularly desirableconversions are accomplished at these temperatures.

Another preferred feature resides in that the gases are cooled when theyhave left the second contacting tray, the gases are reacted in the thirdcontacting tray in contact with a catalyst based on vanadium pentox ide,and the gases leaving the third contacting tray are supplied to thefourth contacting tray without interstage cooling and in the fourthcontacting tray are reacted further in contact with a catalyst based oniron oxide. In these contacting trays, the reactions are carried out inanalogy to those in the first and second contacting trays, respectively,but at the temperatures which are applicable to the third and fourthcontacting trays. These contacting trays may also be arranged one overthe other to form a double contacting tray.

According to a preferred feature, the reaction in the third contactingtray is conducted to a temperature of about 550620C. and the reaction inthe fourth contacting tray is conducted to a temperature of about6307IOC. Particularly desirable conversions are accomplished at thesetemperatures.

In further combined double contacting trays containing catalysts whichare based on vanadium pentoxide and catalysts which are based on ironoxide, the reaction may be continued until the equilibrium temperatureof the gases during the reaction is approximately as high as the maximumtemperature which is permissible for the vanadium catalysts.

The final temperature in the contacting trays which contain catalystbased on iron oxide will depend on the S0 content of the gas whichenters the respective contacting tray. The temperature will shift towardthe upper limit of the stated temperature range in case of a relativelyhigh S0 content and to the lower limit in case of a relatively low S0content.

According to another preferred feature, the catalyst based on vanadiumpentoxide and the catalyst based on iron oxide form two separate layers,which are disposed one over the other on a common grate, and an inertheat-insulating layer, which is permeable to gas, is disposed betweenthe two catalyst layers. As a result, a transfer of heat from thecontacting tray which contains catalyst based on iron oxide to thecatalyst based on vanadium pentoxide is avoided. This is particularlyimportant during a shutdown. Besides, a grate is eliminated which wouldbe subjected to very high temperatures.

According to another preferred feature, the gas is conducted through thecontacting trays from bottom to top so that the gas permeability of thecatalyst bed is not reduced by a deposition of fine solids.

Behind each double contacting tray, the gases leaving the tray areindirectly and/or directly cooled to the operating temperatureprevailing at the inlet of the next contacting tray. In case of arelatively high S0 content, an at least partly indirect cooling isrequired in each case because a cooling effect only by admixingoxygencontaining gases would result in a great increase of the gasvolume. Preferably the cooling is effected indirectly because in thatcase the gas volume will not be increased and constant operatingconditions will be obtained.

The invention is applicable to processes in which the which has beenformed is or is not subjected to interstage absorption.

The invention will now be explained with reference to FIGS. 1 to 3.

In the drawings, the conversion of S0 to 80;, is plotted in dependenceon the gas temperature. Curve g is the equilibrium curve of the reactionS0 /2 0 1: $0

The solid lines 1a to 7a represent the reaction of the gas in thecontacting trays which contain a catalyst based on vanadium pentoxide.

The dotted lines lb and 3b represent the reaction of the gas in thecontacting trays which contain a catalyst based on iron oxide.

The dash-dot lines 10 to 6c represent the interstage cooling steps.

FIG. 1 represents the process for a gas which contains 15% S0 and 8% 0FIG. 2 shows the process for a gas which contains 35% S0 and 20% O FIG.3 shows the process for a gas which contains 60% S0 and 35% 0 Theadvantages of the invention reside in that the number of interstagecooling steps to which the gases must be subjected between thecontacting trays is reduced for a given total conversion so that thecapital requirement and operating costs are much reduced. Besides, thereis a very high temperature difference between the gases to be cooled andthe cooling fluid so that smaller heat exchange surfaces are sufficientfor the indirect cooling.

The catalysts on the basis of V 0 and used in those contacting trays inwhich a deterioration is possible due to the fact that the reaction ofS0 /2 O 7- S0 is not arrested at temperatures of about 620C, may be ofcommercial quality, for example as manufactured by BASF (Catalyst ()4 l0and O4 l l). Preferably the re- 5 activity of the catalysts is decreasedby varying the V content as known for instance from Helv. chim. Akta 24,Reprint No. 71 E 79 E, l3/12, 1941, Basel, Ges. f. chem. lnd.,or by anaddition of reaction retarding substances such as manganese dioxyde asknown from Journal of Catalysis 18 (1970), pages 83-89.?

The catalysts on the basis of iron oxide consist preferably of Fe O asknown ,from Waeser, Handbuch der Schwefelsaurefabrikation,,. l9-30,.pages 1476/77,

The catalysts on the basis of V50 and used in those contacting trays inwhich the reaction SO /2 O 3 S0 is A arrested at. temperatures below,about 620C are of=comrnercial qualityas described above.

, EXAMPLES Example 1 describes FIG. 1, Example 4 describes FIG. 2 andExample 6 describes FIG. 3.

1n Examples 2, 3, 5, 7 and 8 the conversion was conducted until theratio of S0 to $0 was such as to enable a subsequent catalysis to becarried out in known manner. I

The catalysts on the basis of 'V OQand used in those contacting trays inwhich a deterioration by overheating was possible consisted of kieselguras carrier substance with 8 by weight of V 0 and 3 %'by weight of MnO(see Journal of Catalysis 18, (1970), pages 83-89). in the Tables theyare marked with A.

The catalysts on the basis of iron oxide consisted of Fe O (see Waeser,Handbuch der Schwefelsaurefabrikation, 1930, pages 147677). In theTables they are marked with Fe".

The catalyst on the basis of V 0 and used in those contacting trays inwhich a deterioration by overheating was not possible, consisted ofCatalyst 04 l 1 manufactured by BASF. In the Tables they are marked with1B.

in the Tables, columns 1 to 7 contain the following data:

Column 1: Consecutive number of contacting trays Column 2: Type ofcatalyst Column 3: Height of the catalyst in meters Column 4:Temperature of the gas entering the con tacting tray in C Column 5:Temperature of the gas leaving the contacting tray in C Column 6: Totalconversion of the gas as it enters the contacting tray in Column 7:Total conversion of the gas as it leaves the contacting tray in EXAM PLE2 Composition of the gas entering 15.0% $0 the first contacting tray O,

la A V 0,4 440 610 0 38,6 lb Fe 1.0 610 646 38,6 46,8

EXAMPLE 3 Composition of the gas entering 30,0% SO;

the first contacting tray 20,0% 0,

1a 9 A 0.4 440 610 0 21.4 lb Fe 1,0 610 746 21,4 38,4

EXAMPLE 4 Composition of the gas entering 35,0% S0 the first contactingtray 20,0% 0

1a A 0,3 420 610 0 20 lb Fe 1,0 610 719 20 31.5 2a A 0,4 420 610' 31,552 2b Fe 1,0 610 644- 52 59 3a B 0.6 420 578 59 71 4:: B 0,6 420 530 7183 5a B 0,8 420 492 83 6a B 0,8 410 459 90 95,5 7a B 0.8 410 427 95,597,5

EXAMPLE 5 Composition of the gas entering 35,0% SO the first contactingtray 20,0% 0

1a A 0,3 440 610 0 18,7 1b Fe 1,0 610 761 18,7 35,4 2a A 0,4 440 61035,4 43,8 2b Fe 1,0 610 645 43,8 57,6

EXAMPLE 6 Composition of the gas entering 60,0% SO the first contactingtray 35,0% 0,

1a A 0,3 420 610 0 14,0 1b Fe 1,0 610 790 14,0 27,0 2a A 0,4 420 61027,0 41,0 2b Fe 1,0 610 700 41,0 47,5 3a A 0,6 420 610 47,5 61,5 3b Fe0,8 610 638 61,5 63,5 4a B 0,8 420 590 63,5 76,0 5a B 0,8 420 541 76,085,0 6a B 0,8 410 490 85,0 91,0 7a B 0,8 410 478 91,0 94,5

EXAMPLE 7 Composition of the gas entering 55.0%

the first contacting tray 30,07: 0

la A 0,3 4,40 620 O l4,l lb Fe 1,0 620 767 l4.l 25.7 221 A v 0.4 440 62025,7 39,5 2b Fe 1.0 620 717 39,5 47,0 32! A 0,6 440 600 47,0 59.1 3b Fe0.8 600 641 59,1 62,

EXAMPLE 8 Composition of the gas entering 60,0% S0 the first contactingtray 350% 0 la A 0.3 440 620 0 135 lb Fe 1,0 620 762 l3,5 24,2 2a A 0,4440 620 24,2 37,3 2b Fe l,0 620 736 37,3 45,7 3a A 0,6 440 6l0 45,7 57,83b Fe 0.8 6l0 657 57,8 6l,l

What is claimed is:

1. Process for catalytically reacting gases containing 1 l-60% S0 withoxygen in catalyst contacting trays to form S0 wherein the catalyst inthe first contacting trays is different from the catalyst in the secondcontacting tray which comprises reacting said gases in the firstcontacting tray in contact with a vanadium pentoxide based catalyst andfeeding the effluent gases from the first contacting tray to the secondcontacting tray without cooling and reacting said effluent gases thereinin contact with an iron oxide based catalyst.

2. Process of claim 1 wherein the reaction in the first contacting trayis carried out until a temperature of about 550620C. is reached and thereaction in the second contacting tray is carried out until atemperature of about 690760C is reached.

3. Process of claim 1 wherein effluent gases from the second contactingtray are cooled are reacted in a third contacting tray in contact with avanadium pentoxide based catalyst and the effluent gases from the thirdcontacting tray are fed to a fourth contacting tray without cooling andare reacted therein contact with an iron oxide based catalyst.

4. Process of claim 3 wherein the reaction in the third contacting trayis carried out to a temperature of about 55O 62OC. and the reaction inthe fourth contacting tray is carried out to a temperature of about6307l0C.

5. Process of claim 1 wherein the vanadium pentoxide and the iron oxidecatalysts are in two separate layers one over the other on a commongrate with an inert, gas permeable, heat-insulating layer therebetween.

6. Process of claim 1 wherein the gases are conducted through thecontacting trays from bottom to

1. PROCESS FOR CATALYTICALLY REACTING GASES CONTAINING 11*-60*% SO2 WITHOXYGEN IN CATALYST CONTACTING TRAYS TO FORM SO3, WHEREIN THE CATALYST INTHE FIRST CONTACTING TRAYS IS DIFFER ENT FROM THE CATALYST IN THE SECONDCONTACTING TRAY WHICH COMPRISES REACTING SAID GASES IN THE FIRSTCONTACTING TRAY IN CONTACT WITH A VANDIUM PENTOXIDE BASED CATALYST ANDFEEDING THE EFFLUENT GASES FROM THE FIRST CONTACTING TRAY TO THE SECONDCONTACTING TRAY WITHOUT COOLING AND REACTING SAID EFFLUENT GASES THEREININ CONTENT WITH AN IRON OXIDE BASED CATALYST.
 2. Process of claim 1wherein the reaction in the first contacting tray is carried out until atemperature of about 550*-620*C. is reached and the reaction in thesecond contacting tray is carried out until a temperature of about690*-760*C is reached.
 3. Process of claim 1 wherein effluent gases fromthe second contacting tray are cooled are reacted in a third contactingtray in contact with a vanadium pentoxide based catalyst and theeffluent gases from the third contacting tray are fed to a fourthcontacting tray without cooling and are reacted therein contact with aniron oxide based catalyst.
 4. Process of claim 3 wherein the reaction inthe third contacting tray is carried out to a temperature of about550*-620*C. and the reaction in the fourth contacting tray is carriedout to a temperature of about 630*-710*C.
 5. Process of claim 1 whereinthe vanadium pentoxide and the iron oxide catalysts are in two separatelayers one over the other on a common grate with an inert, gaspermeable, heat-insulating layer therebetween.
 6. Process of claim 1wherein the gases are conducted through the contacting trays from bottomto top.